The invention relates to apparatus for shaping tubular members or joining tubular members to another member, such as a tubeplate by expansion of the tubular member.
By tubeplate is meant any tubeplate as such or the wall of a header, drum or other component to which a tube or tubes are joined.
It has already been proposed in U.S. patent specification No. 4,006,619 to expand a tube by axially compressing an annular body of rubber or other elastomeric material within the tube by mechanically applied force so as to produce radial expansion of the body. In that method the annular body is supported at its ends by respective annular arrays of separate metal segments, with open gaps between them.
In that method, the tube is expanded only outside the tubeplate and the tubeplate is not stressed beyond its elastic limit by the expansion of the body of elastomeric material.
In that proposal, the segments which support the body of elastomeric material at its ends have faces engaging the elastomeric material which are inclined so as to restrict the radial expansion of the elastomeric material adjacent its ends. Furthermore, in that proposal, the body of elastomeric material is required merely to stress only the tube beyond its elastic limit. The tube-plate is not stressed or is only slightly stressed elastically. The tubeplate is not stressed beyond its elastic limit.
As explained in U.S. Pat. No. 4,006,619, a problem arises in that the elastomeric material tends to extrude through the gaps between the segments. In any case, until the material has extruded into the gaps only relatively low pressure can be generated in the material and part of the stroke of the tool which applies the load is effectively wasted.
The presence of such gaps gives rise to several drawbacks among which are the damage to the material as it extrudes into the gaps, which means that the material must be replaced after each expansion or after only one or two expansions; and the gaps cannot be maintained equal so that excessive extrusion can occur at one excessively large gap.
For certain applications it is required to apply relatively high pressure to the tube, in which cases the presence of empty gaps into which the material can flow cannot be tolerated at all.
Where it is required to apply sufficient force to stress the tubeplate beyond its elastic limit and to achieve sufficient residual stress in the tubeplate to ensure adequate holding force on the tube, very high applied pressures have to be used approaching 70,000 pounds per square inch (4830) bar.
Furthermore, tolerances on the tube or on the hole or on both may give rise to an annular clearance between the inner surface of the tube and the outer diameter of the main parts of the tool between which the elastomeric body is compressed as large as 0.10 inch (2.54 millimeters).
The tendency for the elastomeric material to extrude at such pressure is even greater and the supports at the ends of the body must not only be able to prevent such extrusion but must not reduce to any pronounced degree the pressure which the elastomeric body is applying to the tube.